Okay drip acclimatization, specifically for adjusting nerites:
1) Get a 5 gallon or larger fish bucket(any plastic bucket or container that has never
had soap or other fish-lethal substances in it)
2) Dump the bag w/snails into the empty bucket. Place bucket next to a large, established freshwater tank.(this process is going to use nearly 5 gallons by the time it's finished)
3) Take a length of air hose between 4 and 6 feet long and tie a loose knot in it.
4) Start a siphon from the tank to the bucket and quickly tighten the knot until the siphon is at a slow
5) Secure the hose so that it won't fall out of the tank or have the tank end come out of the water before you're done. I usually just adjust it to where I want it and close the lid gently.
6) Set an egg timer to check the water level. I usually set it for 30 minutes the first time to see how fast the bucket water level rises and go from there. The slower, the better. You want it to take at least 2 to 3 hours for going from salt to fresh, I usually shoot for 4 to 5. Slo-o-o-o-ow drip.
When the bucket is full, net them out and put them in the tank you siphoned from. Dispose of the water in the bucket and refill the tank as you would for a normal water change. Give them a week to adjust there, then bag 'em up for transfer and normal bag acclimatization is usually fine for their long term tank.
For normal drip acclimatization where you don't have to account for a change in salinity or a big pH difference, two or three gallons and an hour or two is usually fine. The egg timer is basically so you don't forget about it since it takes a while. I forgot once, but fortunately caught it before it flooded too